1. Field of the Invention
The present invention relates to a mask set for measuring an overlapping error and method of measuring an overlapping error using the same. In particular, the present invention relates to a mask set for measuring an overlapping error and method of measuring an overlapping error which can identify an degree of overlapping error generated in all directions during the photolithography developing process and also can easily determine whether an overlapping error occurs or not even using a microscope having a low magnifying power.
2. Description of the Prior Art
As the integration of the semiconductor device becomes higher and smaller, the degree of overlapping alignment between an underlying layer and an upper layer or between an underlying layer and an impurity diffusion layer becomes an important factor in reliability of the device. Accordingly, a mask, on which a mark for measuring an overlapping error is formed, is commonly used to measure the degree of overlapping alignment.
FIG. 1 shows a conventional mask for measuring an overlapping error.
The mask for measuring an overlapping error is consisted of main patterns 1 and sub patterns 2 formed in the upper and underlying layer These patterns can measure an overlapping error created in only one direction of the X-axis or Y-axis direction. However, in case that an overlapping error created in both directions is measured, a measure operation are performed twice by this pattern. In addition, when a microscope having a high magnifying power is used and the patterns become more fined, a measuring error occurs frequently due to aberration of a lens and difference of a measuring point (eye) and a determining point of the measuring scale. Accordingly, although dedicated measurement equipments has been developed, there are problems that they are expensive in cost and a processing time is delayed.
It is an object of the present invention to provide a mask set for measuring an overlapping error which can identify an overlapping error generated not only in the X-axis and Y-axis directions but also in all directions during the photolithography developing process and also can easily determine an overlapping error even using a microscope having a low magnifying power.
To achieve these objects, a mask set for measuring an overlapping error according to the invention comprises a first mask consisted of a mask substrate on which a plurality of unit patterns are formed. The plurality of unit patterns are arranged in radial shape round a given center.
The mask set of the present invention further comprises a second mask consisted of a mask substrate on which a plurality of unit patterns are formed. The plurality of unit patterns of the second mask are arranged in same shape as the plurality of unit patterns of the first mask, whereby when the first and second masks are overlapped to each other, the unit pattern of the first mark and the neighboring unit pattern of the second mask maintains a certain angle.
A method of measuring an overlapping error according to the present invention comprises the steps of forming first measuring patterns on a wafer using a first mask on which a plurality of unit patterns are arranged in radial shape round a given center; forming overlapping second measuring patterns on said wafer using a second mask on which a plurality of unit patterns are arranged in same shape as the plurality of unit patterns of the first mask, whereby the first measuring patterns formed by the first mask and the second measuring patterns formed by the second mask maintains a certain angle; identifying an overlapping error between the first measuring patterns and said second measuring patterns; calculating a value of the overlapping error.